This invention generally relates to nondestructive inspection apparatus and more particularly relates to an inspection probe for inspecting a tubular member for anomalies, which tubular member may be a nuclear steam generator heat exchange tube having an irregularly-shaped interior surface.
However, before describing the subject matter of the present invention, it is instructive first to briefly discuss the structure and operation of a typical nuclear steam generator, which contains a plurality of U-shaped heat exchange tubes. In this regard, a nuclear steam generator is a device for generating steam as heat is transferred from a radioactive primary fluid (i.e., water) to a non-radioactive secondary fluid (i.e., water) across a heat conductor boundary separating the primary fluid from the secondary fluid. The primary fluid flows through the tubes, which function as the heat conductor boundary, as the secondary fluid surrounds the tubes. Each tube is supported along its length by a plurality of tube support plates having holes therethrough for receiving each tube. Moreover, the ends of each U-shaped tube are supported by a tube sheet having apertures therethrough for receiving each tube. Although each tube matingly passes through holes and apertures in the support plates and tube sheet, respectively, a relatively small annular gap may nonetheless exist at the interface of the tube and support plate and at the interface of the tube and tube sheet.
As stated hereinabove, the primary fluid flowing in the tubes is radioactive; hence, for safety reasons the steam generator is designed such that the radioactive primary fluid does not radioactively contaminate the non-radioactive secondary fluid by co-mingling with the secondary fluid. It is therefore desirable that the tubes remain leak-tight during operation of the steam generator so that the radioactive primary fluid remains everywhere separated from the non-radioactive secondary fluid to avoid co-mingling the primary fluid with the secondary fluid.
Occasionally, however, the steam generator tubes may develop surface and volume anomalies (i.e., flaws and tube wall thinning) and thus may not remain leak-tight. Such anomalies may be caused by vibration and by intragranular cracking due to stress and corrosion during operation. If through-wall anomalies are present, the primary fluid may co-mingle with the secondary fluid. Such through-wall anomalies typically occur, if at all, in a tube portion adjacent the gap due to the flow-induced tube vibration and intragranular stress corrosion cracking at that location. That is, the flow-induced vibration of the tube against the support plate or against the tube sheet may lead to wearing of the tube wall. Moreover, potentially corrosive contaminants, which usually appear in the form of sludge deposits comprising iron oxides, copper compounds, and other metals, may settle out of the secondary fluid onto the tube sheet and support plates and then migrate into the gap to constrict, stress and corrode the tube and thus lead to the stress corrosion cracking previously mentioned. Therefore, it is desirable to inspect the tubes for anomalies that are indicative of incipient flaws or through-wall cracks caused by vibration and/or stress corrosion cracking. Such an inspection is usually performed by engaging a suitable radially rotating sensor with the inside surface of the tube. Once such incipient flaws or through-wall cracks are discovered during the inspection process, the tube is either sleeved at the location of the anomaly or plugged, in a manner well known in the art, to prevent the primary fluid from co-mingling with the secondary fluid.
However, the steam generator tube being inspected may have an interior surface that is out-of-round or slightly irregularly-shaped, particularly at the site of the anomaly. The operator of the inspection probe therefore may encounter difficulty inspecting such a tube that is not perfectly round. That is, the irregular shape of the inside surface of the tube may cause the sensor previously mentioned to disengage or lose contact with a portion of the inside surface of the tube as the sensor rotates within the tube. This result is undesirable because each time the sensor loses contact with the inside surface of the tube, the inspection signal generated by the sensor is interrupted. This necessarily causes the operator of the inspection device to reinspect the tube in order to achieve an acceptable inspection signal. Such reinspection increases the time for completing the inspection process. Of course, increasing the time necessary for inspecting the tube increases inspection costs. It is therefore desirable to perform the inspection of the tube using an inspecting device that will allow the sensor to remain in continuous contact with the inside surface of the tube, even though the inside surface of the tube is irregularly-shaped.
Inspection devices for inspecting tubing are known. One such device is disclosed in U.S. Pat. No. 4,937,524 entitled "Rotating Eddy Current Roller Head For Inspecting Tubing" issued Jun. 26, 1991 to Floyd A. Fasnacht et al. This patent discloses a rotating eddy current roller head for inspecting a tube. The device includes a main body portion having a set of wheels attached thereto which center the main body portion in the tube. A roller housing, which is slidably mounted on the main body portion for radial movement relative thereto, is caused to track the surface of the tube by action of opposing magnets mounted in the main body portion and roller housing. An eddy current coil is mounted in a coil holder, which is pivotally mounted at the exterior end of the roller housing, and a spring is mounted in the roller housing to bias the coil holder against the surface of the tube for maintaining the eddy current coil at a constant distance from the surface of the tube during the inspection process. Although this patent discloses an eddy current coil mounted in a coil holder which is pivotably mounted at the end of a roller housing and a spring mounted in the roller housing to bias the coil holder against the surface of the tube, this patent does not appear to disclose an inspection probe for suitably inspecting tubular members that are out-of-round, as described and claimed herein.
Another eddy current inspection device is disclosed in U.S. Pat. No. 4,625,165 entitled "Tube Inspection Probe With Rotating Eddy Current Coil" issued Nov. 25, 1986 to Samuel Rothstein. This patent discloses an electro-mechanical eddy current probe having a rotatable sensing head for sensing the wall thickness of and locating local defects in a tube or conduit through which it is passed. The rotatable head of this device includes a radially movable, outward projecting sensing member which is spring-biased into engagement with the interior surface of the tube and which carries an eddy current coil electrically monitored by the probe. Although this patent discloses a radially movable, outward projecting sensing member which is spring-biased into engagement with the interior surface of the tube, this patent does not appear to disclose an inspection probe for suitably inspecting tubular members that are out-of-round, as described and claimed herein.
Therefore, what is needed is an inspection probe for inspecting a tubular member for anomalies, wherein the tubular member has an out-of-round interior surface.